In the manufacture of motor vehicle drivetrain subassemblies such as transmissions and four wheel drive transfer cases, it is often necessary to utilize cylindrical members including external teeth or splines to act as pinion gears and other components. One common method of forming external splines on a cylindrical workpiece involves rolling the workpiece under pressure between a pair of elongated spline racks including a plurality of teeth located generally transverse relative to the direction of movement of each spline rack. In particular, the spline racks are connected to a machine known as a spline rack cutter that moves each spline rack along a path in the direction of its longitudinal axis in a direction opposite the other spline rack while the cylindrical workpiece is located between the pair of spline racks. In this manner, the plurality of teeth on each spline rack engage the workpiece and form teeth in the surface thereof.
In manufacturing gears such as pinion gears, it is often necessary to form the splines on a smaller diameter region of a workpiece, immediately adjacent to a larger diameter region of the workpiece. The larger diameter region therefore creates a shoulder that can interfere with the spline rolling operations. In order to form teeth on a workpiece as close to the shoulder as possible, prior spline rack cutters have utilized teeth having a chamfered inner corner such that the planar top land surface of each spline rack tooth was connected to the inner edge region of each tooth by means of a chamfer. While this prior design facilitated forming teeth on a workpiece close to the shoulder of the workpiece, the teeth formed on the workpiece were not as strong as desired. Also, the corner of each spline rack tooth formed by the intersection of the planar top land surface and the chamfered inner edge region was found to be susceptible to chipping.
Another attempted solution has involved utilizing spline rack teeth wherein the inner edge region of each tooth is joined to the top land surface by means of a continuous curve. This curved or rounded inner comer region of each spline rack tooth forms teeth on the workpiece such that the bottom land or valley region between each tooth formed on the workpiece curves upward and into the shoulder. This curved transition surface between the shoulder of the workpiece and the bottom land region found between each tooth formed on the workpiece has been found to increase the strength of the teeth formed on the workpiece. Also, these spline rack teeth having rounded inner corners have been found to be less susceptible to chipping relative to the chamfered teeth discussed above.
The curvature of the inner comers of these prior spline rack teeth has heretofore been required to be a relatively sharp to prevent the inner edge region of each spline rack tooth from contacting and/or otherwise interfering with the shoulder of the workpiece. One prior attempt to provide spline rack teeth with more gradually curved inner corner regions involved changing the diameter of the workpiece to "lower" the shoulder. However, this is often not possible due to design requirements such as the strength of the workpiece, or the relationship of the workpiece to other components in the final product.